This invention relates to pushbutton switches. In particular, the invention relates to pushbutton switches wherein the pretravel, i.e. the distance a movable contact travels to engage the stationary contacts, is adjustable to compensate for tolerance accumulations in the parts.
Pushbutton switches generally comprise a housing, a plunger in the housing carrying a movable contact, stationary contacts in the housing aligned with the movable contact, and springs biasing the movable contact and the plunger away from the stationary contacts. Depression of the plunger moves the movable contact into engagement with the stationary contacts to complete an electrical circuit therethrough. The individual parts and significant features of the parts are dimensioned to establish a specific initial dimension between the movable and the stationary contacts in the extended position of the pushbutton, thereby defining a particular distance the plunger must be depressed before effecting engagement of the movable and stationary contacts. Each part and feature dimension has a manufacturing tolerance. When a plurality of parts are involved, the tolerances may "stack" adversely, thereby significantly changing the initial dimension between the movable and stationary contacts in the extended position and therefore changing the distance the plunger must travel to effect contact engagement. In certain end user applications, consistency of this initial dimension between the movable and stationary contacts is essential.